Electrochemical capacitors such as electric double layer capacitors utilize a capacity due to an electric double layer generated at an electrode electrolytic solution interface of a polarizable electrode. In general, the polarizable electrode is formed by using a porous carbon material as a constituent material.
Electrochemical capacitors such as electric double layer capacitors can easily reduce their size and weight, and thus are expected to become backup power supplies for power supplies of portable devices (small-size electronic devices) and the like and auxiliary power supplies for hybrid cars, for example, whereby various studies have been under way for improving their performances.
Proposed as examples of the above-mentioned studies include an electric double layer capacitor aimed at improving its performances by adjusting specific surface areas of carbon materials used in its anode and cathode to respective predetermined ranges (see, for example, the following Japanese Patent Application Laid-Open No. HEI 8-107047) and an electric double layer capacitor comprising an electrode formed by using a plurality of species of activated carbon having respective characteristics different from each other (e.g., a mixture of activated carbon with a lower internal resistance and activated carbon having a large capacitance or energy density) so as to improve its performances (see, for example, the following Japanese Patent Application Laid-Open No. 2000-353642).